Ok all my research has shown that stoichiometric for E85 is about 9.765:1. Now, a standard nb O2 is set up for 14.63:1, and when in closed loop it shoots for that value, the .500v mark. My questions to you guys:

A) Does an O2 read lambda as .500 or 14.63 as .500? If its measuring how much oxygen passes by it, then it should read how far off from lambda (ideal combustion) it is and not 14.63.

If it read 14.63 then:
B) If running E85 at 14.7:1 in closed loop, would that be safe? How would the engine react to running that lean, especially since we know during closed loop the car probably sees anywhere from 11-16:1 as it oscilates rich/lean? Apparently people have used normal O2s when running E85, is it because the higher octane (somewhere around 105-110 from different things I've seen on the internet) keeps the combustion temps down?

C) Adjusting the Stoichiometric value in our VCMs just changes the open loop values when applying open loop/ pe modifiers, at least in this aspect. There is no way to change the target AFR your narrowbands look at unless you have an O2 sensor calibrated for a specific fuel/AFR. If 14.7 reads .5 volts then thats it, no scaling to be done right? Its a hardware thing not a software thing correct?

D) Do they make a specific O2 sensor for running alternative fuels or do you just run with what you got?

If the O2 reads lambda (which after reflecting on how it works I think it should read lambda, because its looking for oxygen that didn't get consumed right, it has no ability to measure how much oxygen per volume, just how much oxygen, correct)

Then closed loop should be pretty solid. You would have to change the stoichiometric value so your open loop commanded AFR would be down to 7 or 8.


I've been trying to find some answers, and there is actually a good bit of info out there, just nothing really technical beyond 'it works with stock o2 sensors' without an explanation of why or how.

My engine is about 12:1 scr and I believe over 9:1 dcr, so I don't really want to take a chance at running it too lean cruising around, it would suck to melt valves n **** just to find out that 'no, the stock O2 sensors really don't work with E85, in high compression applications'.

Interesting information I have found in my searching of the internet, take it for what its worth, if anyone has better knowledge:

1)Stoich is 9.765:1, 7.5 or so would compare to about 12.9 I would guess

2)Apparently people have run E85 in stock OBD2 setups for over two years with no ill effects

3)Apparently although our fuel systems are designed for E10 they can handle much more ethanol than that

4)You will always lose gas mileage running E85, face it, if your optimal AFR is ~10:1 and wot is 7.5:1, its burning more gas.

5)Emmissions is very very less, but catalytics take longer to heat up with E85 so cold start emmisions are about the same and possibly worse. Allegedly there is occasional catylitc converter problems with E85. I don't really care since I don't have cats, but food for thought.

6)Running E85 might cause an SES and keep the car out of closed loop, I don't see how this could happen but it has been alleged.

I'm not sure how true any of those things are, its just stuff I found browsing around, anyone know better?

Thanks

Ben

 

Damn, I would probably need at least 42lb injectors just to support 400rwhp at 7.5-8:1 AFR...

 

This is a good topic, based on the chemical formulas, pure alcohol should provide about a 15% increase in HP due to the oxygen increase in the fuel. At an 85% blend, this is still a 12-13% increase. That's nearly 50hp on a 400 hp car !

 

The 02 sensors should be reading lambda

There's been a few posts about E85 ... seems the gas stations try to make a killing on it so they overprice it (they price it close to the cost of regular ... but since it's less efficient than gasoline you spend more to go fewer miles)


Ethanol can and does make more power than gasoline... but the problem is (as the original posted noted) you need HUGE injectors ... it takes alot more fuel since ethanol isn't as efficient as gasoline ... Another benefit of ethanol is it's something like 110 or 105 octane ... so great for FI cars... but again , you run into injector size issues

 

We can do big injectors

 

Yeah, I've read about every E85 post, just some things don't always seem clear.. heh..

My interest is simply that there is an E85 station a couple blocks from my house, it isn't priced outrageously, and with my compression I usually run 3:1 91/100 mix and I have to drive about 20 miles to get the 100 octane, but if I can just drive down the block and pick up 110 octane then I'd be much happier...

 

theres also a setting in the controller that you can edit with the LM programer software to make itso it reads properly for diferent fuels..cant remember if E85 was in there...but I think it was...I'll look later today as I am not near the ca;e I need to do this)

 

Some facts, and math stuffs.
Ethanol, per gallon, makes 30-40% LESS power than gas. However, it contains its own oxygen, so you can burn much more of it (Air/Fuel Ratio). By the time your done, its almost back to parity with gas. HOWEVER! Ethanol has a higher octane ratio as mentioned, so you can run higher compression, more boost, more timing, and assuming your fuel system can hang, in the end you can make more power, if the motor is built to run it. Since right now prices aren't that good, its not really worth it in my opinion. The good thing about it though, is you can make your own

 

It may be easiest to instal a wideband O2 sensor and use this to tune for open loop speed density (open loop MAF-less) using the AFR you quoted.

 

OK, one of the guys at work is very interested in this topic (he has an E85 Dodge minivan and is interested in running his Jeep on E85). We looked at the factory service manual for his minivan, and they only use one 02 sensor. There are no other additional sensors to tell the pcm that you are running E85. System is a Speed Density system, as there is no MAF.

The question is how does it know when it is running E85 and how does it know when it is running gas ?

2 possibilities:

1. LTFT limits must be a lot wider, allowing the LTFT's to adjust the fuel that is being run better

2. 2 different fuel algorithims, when the LTFT's using one algorithim exceed a certain value, it switches to the other one.

I tend to think it must be #2, because #1 just doesn't seem to make sense. Can anyone think of any other possibilities ?

Either way, it does make the case that we should be able to run E85 and have closed loop work just fine, merely by adjusting the Stoich value and the PE AFR.

As someone mentioned, could be easily verified using an LM1. BTW, it does not have an E85 setting, but it does allow custom setting of Lamda-Stoich AFR.

I won't be able to test this on my car as it is getting put away for the winter this weekend, however someone who either drives theirs in the winter or lives down south should test this.

Could be a really big benefit for FI guys - turn up the boost !!!

 

Flex fuel vehicles have a sensor to determine the approximate alcohol content. This percentage is then used to interpolate between stochiometric values for the different fuels based on tables in the pcm.

 

What sort of sensor, I went through the entire factory manual and found no mention of any special sensor ??

 

I have driven my car on 60% E85 all summer without problems, I have bought bigger injectors now so i can drive 100% E85... I am in Speed Density and tuning with hptuners.

 

What changes did you make to compesnate for different stoichiometric values?

 

All i have done so far is ad to the VE-table.

 

You dont need to adjust the stoich or the AFR.
scale the injector map and adjust the VE, should be all you have to do.
maybe add some more timing.

 

That doesn't make any sense.

The vehicle uses stoichiometric to calculate fueling requirements at WOT via the PE Ratio.

E85 has a different AFR requirement at WOT.

Scaling the injectors just gives the computer innaccurate data in regards to how much fuel it is supplying. It might get you were you want to be, but would be the backwards way of doing it.

All you have to do is change stochiometric to 9.765:1. Make sure your PE brings your WOT AFR down to between 6.9 and 8.5 to 1. No need to change any fueling requirements for part throttle as your o2s measure lambda.

 

Exactly VE=airflow and changing the fuel will not affect airflow.
steelchicken are you talking about scaling the injectors to adjust the AFR or recalculating the IFR table for larger injectors?

 

Agreed on the AFR, but what if you want to switch back and forth between E85 and Gas ? I mean, how do the E85 cars know what is in the tank ?

 

Flex fuel GM vehicles have a sensor in the fuel line that tells the pcm what level of ethanol is in the fuel. I would *guess* it figures the specific gravity of the fuel at any given time .